Chemistry Past Paper 2025 PDF

# Chemistry ## Tips and Tricks - Number of elements in a single transition series = 10 elements - Number of transition elements in a series = 9 elements - Number of elements in the lanthanide or actinide series = 14 elements - Number of inner transition elements in the lanthanide or actinide serie...

# Chemistry ## Tips and Tricks - Number of elements in a single transition series = 10 elements - Number of transition elements in a series = 9 elements - Number of elements in the lanthanide or actinide series = 14 elements - Number of inner transition elements in the lanthanide or actinide series = 13 elements - Total number of main transition elements in the periodic table = 4 x 9 = 36 elements - Total number of inner transition elements in the periodic table = 2 x 13 = 26 elements ## First Transition Series * This series includes 10 elements. * The elements in this series are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. | Element | Symbol | Atomic Number | % by weight | | -------- | -------- | -------- | -------- | | Scandium | Sc | 21 | 0.0026 | | Titanium | Ti | 22 | 0.66 | | Vanadium | V | 23 | 0.02 | | Chromium | Cr | 24 | 0.014 | | Manganese | Mn | 25 | 0.11 | | Iron | Fe | 26 | 5.1 | | Cobalt | Co | 27 | 0.003 | | Nickel | Ni | 28 | 0.0089 | | Copper | Cu | 29 | 0.0068 | | Zinc | Zn | 30 | 0.0078 | * The table above shows that the total percentage of the elements in the first transition series is less than 7 % of the Earth's crust. However, they are very important economically. ## Important Compounds ### Manganese 1. **Manganese Dioxide (MnO2)** Is a strong oxidizing agent, used for making dry cells. In dry cells, chemical energy gets converted into electrical energy. 2. **Potassium Permanganate (KMnO4)**: Used as an oxidizing agent by chemists and as an antiseptic by doctors, it can also be used for disinfecting swimming pools and fish tanks, as well as washing vegetables. 3. **Manganese Sulphate (MnSO4)**: Used as a fungicide, for example, treating skin diseases (tinea) and spraying crops. ### Iron (Fe26) 1. Used in reinforced concrete and electricity towers. 2. Used in the manufacture of knives, gun barrels, cannons, surgical tools, and surgical instruments. 3. A catalyst in: - The production of ammonia by the Haber-Bosch process. - Converting carbon monoxide and hydrogen gas mixture into liquid fuel by the Fischer-Tropsch method. * The Fischer-Tropsch method, the distance between molecules decreases, and the force of attraction is increased. Some examples of liquid fuels are methyl alcohol and octane. ### Cobalt (Co27) - Used in magnets manufacturing and dry batteries (lithium-ion batteries) in modern cars. - In dry batteries, chemical energy is converted into electrical energy. #### Properties - Similar like iron because both are magnetic. - Cobalt has 12 isotopes, the most important is Cobalt (60). #### Uses - Used in preserving food and other applications. - To ensure the quality of products, because it detects cracks and welds. - Used for detecting and treating cancer. - It emits gamma rays which have high penetration power. ### Vanadium (V23) - Used in spring alloys for car springs. Why? Because adding a small amount of vanadium produces an alloy with high hardness, strength, elasticity, and resistance to corrosion. This alloy is used for jet engine gears. - Vanadium pentoxide (V2O5) used as pigment in ceramic and glass manufacturing, as a catalyst in superconductors, and in sulfuric acid production and aromatic carboxylic acid preparation. ### Chromium (Cr24) - A highly active element, but it resists atmospheric corrosion. Why? Because a layer of oxide forms on the surface. The size of the oxide molecules is larger than the element's itself. This creates a non-porous surface from the oxide layer, which prevents chromium from reacting further with oxygen. Chromium is therefore said to "rust" but not actually "corrode". - Used for coating metals, tanning leather, and protecting animal skins from decomposition and making them durable. Leather is therefore used in making shoes and leather products. - **Chromium compounds**: - Chromium Oxide (Cr2O3): used as a pigment. - Potassium dichromate (K2Cr207): used as an oxidizing agent. * **Oxidising agent** : "An oxidizing agent is a substance that gains electrons or loses hydrogen, and the substance undergoes reduction. ### Manganese (Mn25) - Used in alloys or compounds but not pure. Why? Because it is very brittle in its pure state. - Alloys: - Manganese alloy with iron: Used for making railway tracks and safes. Why? Because this alloy is stronger than steel. - Manganese alloy with aluminum: Used for making soft drink cans. Why? Because it is resistant to corrosion. ## Economic Importance of the First Transition Series Elements ### Scandium (Sc21) - Found in small quantities widely distributed in the Earth's crust - Used to manufacture mercury vapor lamps. Why? Because it produces efficient light which resembles sunlight. - The alloy of scandium and aluminum is used in MiG fighter jets, bicycle frames, and baseball bats. Why? Because this alloy is light and very hard. ### Titanium (Ti22) - It is as hard as steel but less dense. - The mass of a steel cube is greater than a titanium cube with the same volume. - The volume of a steel cube is greater than a titanium cube with the same mass. - Used for dental implants and artificial joints, as well as in surgical procedures. Why? Because the body does not reject this element and does not cause any poisoning. - Titanium alloy with aluminum: Used in aircraft and spacecraft production. It is also used in protective gear and helmets. Why? Because titanium maintains its strength at high temperatures where aluminum loses its strength. #### Compounds - Titanium dioxide (TiO2): Used to protect from sunlight. Why? Because its fine particles prevent ultraviolet rays from reaching the skin. The mechanism of TiO2 is similar to that of the ozone layer. - TiO2 is used in the manufacture of tinted glasses. ### Nickel (Ni26) - **Properties**: - Nickel alloy with steel: Strong, resistant to corrosion and acids. - Nickel alloy with chromium: Used in heaters and electrical ovens. Why? Because it stands corrosion even when the equipment is red hot. - In this alloy, electrical energy is transformed into thermal energy. - Nickel is used in: - **Notable compounds**: - Nickel-cadmium batteries. - Plating many metals, Why? Because it protects them from oxidation and corrosion, making them more visually appealing. - Finely divided nickel can be used to catalyze hydrogenation reactions. * **For Your Information**: Hydrogenation: converting unsaturated oils into solid saturated fats ### Copper (Cu29) - Historically, it was the first metal known to man.. - Its alloy with tin is called bronze. - Used in coinage and electrical cables. Why? Because it is a good conductor of electricity. - **Important compounds**: - Copper sulphate(CuSO4): Used as an insecticide and fungicide. - Fehling's reagent: Used to detect glucose. The reagent turns from blue to orange. * **For your information**: The Fehling's solution consists of two solutions: an organic salt and blue copper sulfate. ### Zinc (Zn29) - Most of the zinc is used in galvanization to protect other metals from rusting. - *Galvanization:* dipping the metal in molten zinc to protect the metal from corrosion. - **Important compounds**: - Zinc oxide (ZnO): Used in paints, rubber, and cosmetics. - Zinc sulphide (ZnS): Used in the manufacture of luminous paints and x-ray screens. ## Electronic Configuration and Oxidation States | Element | Group | Electronic Configuration | Oxidation States | Common Compounds | | -------- | -------- | -------- | -------- | -------- | | Scandium | IIIB | [Ar] 4s² 3d¹ | 3 | Sc2O3| | Titanium | IVB | [Ar] 4s² 3d² | 0, 3, 2 | TiO2, Ti2O3, TiO | | Vanadium | VB | [Ar] 4s² 3d³ | 0, 4, 3, 2 |V2O5, VO2, V2O3, VO | | Chromium | VIB | [Ar] 4s¹ 3d⁵ | 6 , 0, 2 | CrO3, Cr2O3, CrO | | Manganese | VIIB | [Ar] 4s² 3d⁵ | 7, 6, 0, 3, 2 | MnO2, Mn2O3, MnO, KMnO4, K2MNO4 | | Iron | VIII | [Ar] 4s² 3d⁶ | 6, 0, 2 | Fe2O3, FeO | | Cobalt | VIII | [Ar] 4s² 3d⁷ | 4, 3, 2 |[CoF4]2, CoCl3, CoCl2 | | Nickel | VIII | [Ar] 4s² 3d⁸ | 4, 3, 2 | NiO2, Ni2O3, NiO | | Copper | IB | [Ar] 4s¹ 3d¹⁰ | 2, 1 | CuO, Cu2O | | Zinc | IIB | [Ar] 4s² 3d¹⁰ | 2 | ZnO | **Note**: The oxidation states marked with a circle are the most common. ### Observations on Electronic Configuration 1. The first transition series elements are located in the fourth period after calcium (Ca20) with the electronic configuration of [Ar] 4s². 2. The filling of the 3d subshells starts, following Hund's rule, where each element adds a single electron to each one of the five orbitals in the 3d subshells. 3. The pairing of electrons in each orbital continues until we reach zinc 3d¹⁰.